1. Field of the Invention
The present invention is directed to electric machine external, cooling systems and in particular air cooled systems for circulation of additional cooling air volume and pressure into an alternating current (ac) motor housing.
2. Description of the Prior Art
Electric machines, such as ac motors, generate heat during operation. It is desirable to transfer heat out of the electric machine's housing during operation. In the past motors and other electric machines have been provided with housing vents and internally formed channels to provide housing airflow cooling paths for circulating air in, through and out of the housing. Airflow circulation through the housing airflow cooling paths has been enhanced by addition of housing internal fans, powered by the electric machine's shaft, oriented within the housing and in communication with the housing cooling paths.
While an internal housing fan increases cooling air circulation through an electric machine's housing airflow cooling paths, its pumping capacity is limited by blade size and geometry constraints, such as length, width, blade cross-section, pitch and blade quantity. The internal housing fan diameter is limited to that which fits within the housing's internal diameter envelope. Similarly, blade width and pitch is limited to the axial space constraints within the housing interior.
Another known way to increase electric machine internal, heat transfer capability through housing airflow cooling paths has been to utilize externally powered fans blowing air into motor enclosures. In this way ambient air is drawn into the motor's inlet cooling vents and heated air exiting outlet cooling vents in the housing can be more readily dissipated to ambient air surrounding the motor. Such solutions require additional powered cooling sources or fans outside the motor in the motor room or a new additional motor enclosure. Those solutions require provision for additional power sources to power the external fans or other environmental cooling devices, and possibly new enclosures.
Air-to-cooling fluid heat exchanges have also been employed within electric machine housings, including totally-enclosed motors that recirculate and cool air within a motor housing. Totally-enclosed motors are often installed in harsh environmental surroundings (e.g., corrosive, abrasive or other solid dust contaminants, fouling sprays, electrically conductive dust, and explosive vapor/dusts). In totally-enclosed motors, heated air in the housing airflow cooling path transfers heat to an internal heat exchanger, and in turn the heat is transferred to a circulating cooling fluid. As with internal housing fans, internally mounted heat exchanger heat transfer capacity is limited by the size of exchanger that can be enclosed within the motor housing.
Thus a need exists in the art for an electric machine cooling system whose airflow cooling capacity is not limited by the size of cooling components contained within the machine's housing.
A need also exists in the art for an electric machine cooling system that does not require an external power source outside the machine housing to increase airflow cooling capacity, as is required when external fans or air conditioning equipment is installed in a motor room or enclosure in order to increase general heat transfer capacity of surrounding ambient air.
Another need exists in the art for an electric machine cooling system that increases airflow cooling capacity, yet that can be retrofitted to existing electric machine designs, including open-vented or totally-enclosed motors. Further, it is desired that the retrofit capability to fulfill this need be implemented any time during manufacture, at existing field installation sites, or during maintenance overhauls in repair shops.